1. Field of the Invention
The present invention relates generally to storage area networks.
2. Description of the Related Art
The management of information is becoming an increasingly daunting task in today's environment of data intensive industries and applications. More particularly, the management of raw data storage is becoming more cumbersome and difficult as more companies and individuals are faced with larger and larger amounts of data that must be effectively, efficiently, and reliably maintained. Entities continue to face the necessity of adding more storage, servicing more users, and providing access to more data for larger numbers of users.
The concept of storage area networks or SANs has gained popularity in recent years to meet these increasing demands. Although various definitions of a SAN exist, a SAN can generally be considered a network whose primary purpose is the transfer of data between computer systems and storage elements and among storage elements. A SAN can form an essentially independent network that does not have the same bandwidth limitations as many of its direct-connect counterparts including storage devices connected directly to servers (e.g., with a SCSI connection) and storage devices added directly to a local area network (LAN) using traditional Ethernet interfaces, for example.
In a SAN environment, targets, which can include storage devices (e.g., tape drives and RAID arrays) and other devices capable of storing data, and initiators, which can included servers, personal computing devices, and other devices capable of providing write commands and requests, are generally interconnected via various switches and/or appliances. The connections to the switches and appliances are usually Fibre Channel.
A typical appliance may receive and store data within the appliance, then, with an internal processor for example, analyze and operate on the data in order to forward the data to the appropriate target(s). Such store-and-forward processing can slow down data access, including the times for reading data from and writing data to the storage device(s). Accordingly, switches are often used to connect initiators with appliances, given the large number of initiators and small number of ports included in many appliances. In more current SAN implementations, switches have replaced certain functionality previously preformed by appliances such that appliances are not necessary and can be eliminated from the systems.
Some storage area networks provide for replicating data from a first storage location to a second storage location. Such replication includes either a synchronous or asynchronous implementation and is typically performed under the control of a host device such as a server or under the control of a storage subsystem. Synchronous based replication by a host device is performed at the application or file level such that each write by the host device to a volume is simultaneously broadcast or replicated to both a primary and secondary location. Synchronous replication can have deleterious effects on application performance because applications must wait for an indication that a write has been successfully completed at each location before proceeding. While host based asynchronous replication can be performed at distinct points in time from writing the initial data to the primary location, it also presents problems. Asynchronous replication is typically performed at the application or file level as with host based synchronous replication. Accordingly, precise logic must be implemented to maintain consistency such as proper order of access requests to the replicating volume. Furthermore, host based asynchronous replication generally involves buffering the replicated data in the host device after reading it from a source and before providing it to a destination. Buffering the data increases replication time and consequently degrades system performance.
Accordingly, there is a need for techniques and systems in storage area networks to address these identified deficiencies and provide for switch-based replication that is both efficient and reliable.